Recently, from the viewpoint of environmental maintenance, resource conservation and garbage reduction, the lighter weight and lower weighing of paper are demanded, and therefore the incorporation of various types of fillers at a high proportion of content has been made to improve the brightness, opacity and printability of the paper.
However, in the paper incorporating large amounts of the fillers, the proportion of pulp is relatively lowered, and the fillers inhibit the hydrogen bond between pulp fibers, thus causing a large decreasing in paper strength. In order to retain the paper strength, there are used chemical agents such as paper strength enhancing agents, for example, starch and polyacrylamide (herein after referred to as “PAM”). In order to obtain a large paper strength improving effect, it is necessary to increase the amount of the agents to be added. Under this condition, there may arise the problem such as a lowering of retention, a lowering of sizing property, or contamination.
The following can be referred to as related art where filler subjected to aggregation, adsorption, or coating with a specific component is incorporated into paper for the purposes of paper strength enforcement and the like.
(1) Patent Document 1
It is disclosed that for the purpose of manufacturing a filled paper that reduces deteriorations in paper strength and intensity due to the incorporation of fillers, an acrylic latex is added to a filler suspension to form the agglomerate of fillers in advance, and this is then added to a pulp suspension (that is, the acrylic latex is not added to suspension composed of pulp and fillers) (refer to claim 1, and paragraphs “0001” and “0004”). The acrylic latex is acrylic monomer alone such as (metha)acrylic acid, alkyl(metha)acrylate, hydroxyl group-containing alkyl(metha)acrylate, or latex manufactured by adding other monomer (styrenes, unsaturated dicarboxylic acid, etc), which can be copolymerized with these acrylic monomers (refer to paragraphs “0012” and “0014”).
(2) Patent Document 2
It is disclosed to manufacture paper with high content of filler by wet papermaking using composite particles obtained by coating process of precipitated calcium carbonate with branched amphoteric acrylamide copolymer (PAM) of a specific molecular weight, for the purposes of reducing deterioration in paper strength due to the incorporation of fillers (refer to claim 1, and paragraphs “0001,” “0005,” and “0006”).
(3) Patent Document 3
It is disclosed to use, as filler, one obtained by allowing amphoteric PAM to be adsorbed on calcium carbonate (salt formation, electrostatic coupling, physical adsorption, etc), for the purposes of obtaining a filled paper using calcium carbonate as filler (refer to the scope of claims, and the upper right column to the lower right column on page 2).
(4) Patent Document 4
It is disclosed to manufacture paper having brightness by using inorganic filler obtained by treating an inorganic material such as calcium carbonate with a cellulose derivative such as sodium carboxymethyl cellulose (CMC) (refer to claims 1 to 9, pages 5 to 6, and examples 1A to 1H).
(5) Patent Document 5
It is disclosed to perform wet papermaking by allowing filler to be coagulated with cationic starch and cationic guar gum, and then adding the coagulated filler to pulp slurry, for the purposes of preventing paper strength deterioration, while incorporating a large amount of calcium carbonate (refer to claims 1 to 2, and paragraphs “0004,” “0008” to “0013,” and “0024”).
(6) Patent Document 6
It is disclosed that wet papermaking is made by premixing ground calcium carbonate with cationic modified starch solution, and adding this to pulp slurry (refer to the scope of claims, and page 2, the upper right to the lower right column). It is also described that in this case, anionic polymer such as polyacrylate may be used together with cationic modified starch (refer to the upper left column on page 3).
(7) Patent Document 7
It is described to add a preliminary coagulated filler to pulp slurry (refer to claim 1, and paragraphs 8 and 15), and as floccurant, there are exemplified water-soluble vinyl polymer, gum, PAM, aluminium sulfate, anionic starch derivative, and the like (refer to paragraphs “0016” to “0018”).
Patent document 1: Japanese Unexamined Patent Publication No. 2004-100119
Patent document 2: Japanese Unexamined Patent Publication No. 2004-18323
Patent document 3: Japanese Unexamined Patent Publication No. 59-26595:
Patent document 4: Japanese Unexamined Patent Publication No. 9-505099:
Patent document 5: Japanese Unexamined Patent Application Publication No. 10-60794:
Patent document 6: Japanese Unexamined Patent Application Publication No. 60-119299
Patent document 7: Japanese Unexamined Patent Publication No. 2000-129589